Various methods for extracorporeal blood treatment are known. In hemodialysis (HD), the patient's blood is cleaned in an extracorporeal blood circuit which comprises a dialyzer. The dialyzer comprises a blood chamber and a dialyzing fluid chamber, which are separated by a semipermeable membrane. Whereas dialyzing fluid flows through the dialyzing fluid chamber in hemodialysis (HD), substances being transported through the membrane on account of the diffusion between the dialyzing fluid and the blood, dialyzing fluid does not flow through the dialyzing fluid chamber of the dialyzer in the case of hemofiltration (HF). In the case of hemofiltration (HF), certain substances are effectively removed through the membrane of the filter by convection. Hemodiafiltration (HDF) is a combination of both methods.
In the performance of an extracorporeal blood treatment, there is basically the risk of a rupture of the semipermeable membrane of the dialyzer or filter. The casting compound of the dialyzer or filter can also become detached. In the case of a defect of the dialyzer or filter, blood passes out of the extracorporeal blood circuit into the fluid system of the blood treatment apparatus. With the known blood treatment apparatuses, therefore, the entry of blood into the fluid system due to a defect of the dialyzer or filter is monitored. The detection of blood in the fluid system takes place according to the prior art with an optical measuring method, wherein the reduction in the intensity of light passing through the dialyzing fluid is evaluated. When blood enters into the dialyzing fluid, the intensity of the light exiting from the dialyzing fluid changes, the change in intensity being dependent on the wavelength of the light. An entry of blood into the fluid system can be reliably detected with the known methods.
Apart from the entry of blood into the fluid system due to a defect of the dialyzer or filter, for example due to a membrane rupture or a casting compound detachment, free hemoglobin or its constituents can also get into the dialyzing fluid in an extracorporeal blood treatment due to a hemolysis. Hemolysis denotes the dissolution (destruction) of the erythrocytes (red blood corpuscles) of the blood. The erythrocytes substantially consist of the oxygen-binding protein hemoglobin, which endows the erythrocytes and therefore the blood with the red color. When hemolysis occurs, hemoglobin is released.
In an extracorporeal blood treatment, a hemolysis can occur for example due to a mechanical strain on the blood due to shear flows. Such shear flows occur, amongst other things, when a blood-carrying hose line of the hose line system of the blood treatment apparatus is kinked. A hemolysis can however also be caused systemically due to the patient.
In extracorporeal blood treatment, hemoglobin can also defuse from the blood side of the dialyzer through the semipermeable membrane onto the dialysate side. The hemoglobin can therefore be detected in the blood with the optical measuring methods known according to the prior art.
A drawback is that, with the known optical measuring methods, it is not possible to distinguish between the entry of blood due to a defect of the dialyzer or filter or the entry of hemoglobin as a blood constituent due to a hemolysis. Different measures have to be taken, however, in the case of a defect of the dialyzer or filter or in the case of a hemolysis. Thus, for example, the dialyzer must be replaced in the case of a membrane rupture, whereas in the case of a hemolysis the user must be prompted to take suitable countermeasures, for example to replace the hose system or at least to free it from the kinked point.
The monitoring devices generally used in extracorporeal blood treatment to detect an entry of blood or a hemolysis are based on the spectroscopic evaluation of the red and green component of light. In this wavelength region, however, it is not possible to distinguish between blood and hemoglobin.
US 2007/0259436 A1 describes a method for detecting hemoglobin in the blood, wherein light with a wavelength of 390 to 460 nm passes through a sample. The change in the light intensity is determined for two or more wavelengths.
A method for detecting a hemolysis, wherein the reduction in the intensity of the blue component of light is taken into account, is also known from JP 62000838A.